This invention relates to the field of automatic spray guns for use in an automatic spray gun system, and in particular to a high volume, low pressure (HVLP) spray gun which requires a relatively higher volume of atomizing air at relatively lower pressure.
Prior art spray guns for use in automatic spray systems have been of the assembly-as-a-whole type, wherein the entire spray gun is constructed in such a way that the different working components include integrally formed or connected portions which are in turn part of other working components so that when any one component needs servicing the entire spray gun has to be removed from its setting in the automatic spray system.
The spray gun in accordance with the present invention is particularly unique in that each of the working components of the spray gun has been constructed as a separate module, complete in itself. These modules include first of all the gun body itself having the atomizing air chamber therein and mounting means for mounting in the automatic spray set-up, the needle valve operating piston and cylinder component which is secured to the gun body by two cap screws, the nozzle and nozzle block module to deliver an atomizable liquid through the nozzle orifice which is secured in place within the gun body cavity by a fitting through its cylindrical wall and special construction of the nozzle block housing described in detail later, the atomizing module comprising an air cap, a pattern ring, a detent plate and a compression spring which are secured to the gun body by threading the pattern ring on the front end of the gun body around its open front wall to hold the other parts of this module within the gun body cavity with the compression spring bearing against the nozzle block housing and the detent plate plus air cap sandwiched between the compression spring and air cap, the needle valve module which is not affixed to any other part of the spray gun but has non-fixed operating connections to other parts such as sliding, abutment and the like, wherein it extends through central apertures of the piston and cylinder module, through the gun module and its atomizing air chamber, through the nozzle and nozzle block module with the tapered needle end of the needle valve module extending into the correspondingly tapered nozzle orifice cavity, and the fluid regulating module which is secured to the spray gun by screwing the externally threaded forward end of its cylindrical housing into an internally threaded aperture of the rearwardly facing cover plate of the piston and cylinder module.
Such unique modular construction is of particular commercial importance for spray guns used in robotic or automatic spray set-ups, since the setting of the gun body module itself need never be disturbed in order to service any or all of the other separate, complete in themselves, modules. This not only saves time but even more importantly the distance and angle of the original setting of the gun body can remain exactly the same after servicing of the modules of the modular spray gun in accordance with this invention as before. Thus, the work pieces sprayed after servicing will be exactly the same as those sprayed before, so the finished work products will all have the same uniform appearance.
This is not possible with prior art spray guns which have to be completely removed from their setting within a robotic or automatic spray set up for servicing.
The automatic spray gun in accordance with this invention utilizes a source of pressurized air from a control center, usually operated by a computer, to operate a pneumatic piston and cylinder module for opening the nozzle orifice to start fluid flow by drawing the needle valve module rearwardly when the control source signals such air pressure to flow to the piston and cylinder module and for closing the nozzle orifice to stop fluid flow by signaling such flow of air pressure to stop whereupon a compression spring of the piston and cylinder module biases the piston forwardly and a compression spring of the fluid regulating module biases the needle valve module forwardly to close the nozzle orifice.
By utilizing pressurized air from a control source to both operate and signal operation of the needle valve, the same control source of pressurized air can be utilized to control operation of atomizing air delivered to the spray gun from a different pressurized air source, which can include the feature of continuing flow of atomizing air to the spray gun for a selected time period after the needle valve has been signaled to close so as to make sure that any flow of fluid from the nozzle orifice after the needle valve has been signaled to close, and before it actually does, will be atomized into a spray and will not flow out in an unatomized stream which would ruin the work pieces it falls on. This feature of doubling to also control operation of the atomizing air to the spray gun is the subject of a separate invention, but utilization of a control and operating means for the needle valve of the spray gun which has the capability of being also utilized to control operation of the atomizing air delivered to the spray gun is an important advantage of the spray gun in accordance with this invention over the prior art.
Another improvement over the prior art provided by this invention is the placing of an air pressure gauge at the forward end of the gun body whereby it is possible to simultaneously monitor both the spray on the finished work while it is occurring and the atomizing air pressure within the chamber of the gun body and do so on a continuous basis if desired. It is not necessary to look away from the work in process to see what the air pressure is being delivered to the atomizing air chamber of the spray gun. The ability to place an air pressure gauge at the forward end of the gun body is made possible by the unique construction of the nozzle block housing of the spray gun in accordance with this invention which is described in detail later that permits an air passageway of the atomizing air chamber above the nozzle block housing which must of necessity be located within the forward end portion of the gun body.
Many additional improvements and advantages of the spray gun in accordance with this invention will become apparent from the detail description which follows and from the accompanying drawings.